1. Field of the Invention
The present invention relates to a method to control an optical apparatus that includes a variable optical attenuator (VOA) and a semiconductor optical amplifier (SOA) set in downstream of the VOA.
2. Related Background Arts
An optical communication system sometimes installs an optical apparatus including an SOA between an optical transmitter and an optical receiver. Such an optical apparatus, detecting intensity of an input beam provided from the optical transmitter, adjusts or controls the SOA such that intensity of an output beam amplified by the SOA is set in target intensity, which is often called as the automatic power control (APC). Because the intensity of the input beam temporally varies, the apparatus sometimes attenuates the input beam and then amplifies once attenuated beam to the target intensity by the optical amplifier.
A Japanese patent application laid open No. H08-248455A has disclosed an optical apparatus that includes a front amplifier and a rear amplifier, a VOA put between two amplifiers, a first optical detector for detecting intensity of an amplified beam output from the front amplifier, a second optical detector for detecting intensity of an attenuated beam output from the VOA, and a third detector for detecting intensity of another amplified beam output from the rear amplifier.
The optical apparatus disclosed therein adjusts optical gains of the respective amplifiers and the attenuation of the VOA based on the outputs from the first to third optical detectors. Complex calculations are inevitably required in such an optical apparatus for setting the intensity of the output beam in the target one because respective optical beams each output from the amplifiers and the VOA are detected. Also, the implementation of two or more detectors results in an expanded housing.